As the development of the technology of a thin-film-transistor liquid crystal display panel, the requirement on image quality is becoming higher and higher. Increasing the thickness of the polyimide (PI) film used for preparing an alignment film may improve friction anchoring capacity significantly, and the improved friction capacity may alleviate image sticking caused by the light leakage in a large-sized product. However, an increased thickness of the PI film may cause a problem such as stains in the panel. Since there is a large step at a position of a via-hole, PI is likely to be affected and absorbed into the via-hole during diffusing, which results in conspicuous color mura, and affects the image quality seriously.